Artist's impression of Curiosity guiding its entry into the Martian atmosphere after being exposed to the high-radiation interplanetary environment for 253 days before arriving at Mars on Aug. 5, 2012.
NASA/JPL-Curiosity

A radiation sensor inside NASA’s Curiosity Mars rover shows that even under the best-case scenario and behind shielding currently being designed for NASA’s new deep-space capsule, future travelers will face a huge amount of radiation.

The results, based on Curiosity’s 253-day, 348-million-mile cruise to Mars, indicate an astronaut most likely would exceed the current U.S. lifetime radiation exposure limit during one round trip mission.

“Even for the shortest of missions we are perilously close to the radiation career and health limits that we’ve established for our astronauts,” NASA’s chief medical officer Richard Williams told a National Academy of Sciences’ medical committee on Thursday.

The Institute of Medicine panel is looking into ethics and health standards for long-duration spaceflights.

Curiosity, which landed inside a giant impact basin near the Martian equator on Aug. 5, 2012, continues to collect radiation data as it conducts its primary mission to look for habitats that could have supported ancient or possible present day microbial life.

Curiosity’s Radiation Assessment Detector, known as RAD, measures the amount and energy levels of highly energetic particles in galactic cosmic rays and from the sun. Scientists then converted the data into radiation dosage units known as sieverts, which are associated with increased cancer risk.

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Current U.S. standards limit an astronaut’s lifetime radiation exposure to 1 Sievert, or 1,000 milliSieverts, which equates to about a five percent chance increase in developing a fatal cancer.

A new study shows that with currently available propulsion technologies and similar shielding to Curiosity’s, astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts and that doesn’t include radiation dosages for any time spent on the Martian surface.

“We have a challenge,” Williams said during a webcast meeting on Thursday of the spaceflight health and medical ethics committee.

“We have the probability that in pursuing exploration-class missions beyond low-Earth orbit of long-duration that we will exceed the standards that we have already promulgated inside the agency. We need the advice of the committee on how best to go about proactively resolving some of these potential conflicts,” Williams said.

In general, Curiosity’s shielding was more effective against particles emitted during solar storms, known as coronal mass ejections, than galactic cosmic rays.

“The galactic cosmic ray, during cruise, is the most dangerous. It’s certainly very high energy and it doesn’t go away. On the surface, you have some atmospheric protection and obviously it depends on how long you stay on the surface,” RAD lead scientist Donald Hassler, with the Southwest Research Institute in Boulder, Colo., told Discovery News.

“It’s more difficult to shield against the galactic cosmic rays. The only mission design strategy for that is just to get there as fast as you can. The solar particle events give you more opportunity to potentially shield against them, however, what we’re finding is that even these events potentially can contribute significantly to the total radiation dose an astronaut may experience,” Hassler said.

During the cruise phase, RAD detected five solar particle events, which accounted for about five percent of the total radiation dose during the trip to Mars.

“In a different year, in a different time in the solar cycle, this percentage might be greater or less. It could be 25 percent or its could be zero,” Hassler said.

A second paper describing Curiosity’s radiation measurements on the Martian surface has been submitted to Science, which published the team’s initial results in this week’s issue.

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